FCL (Framework Class Library) :
A library of functionality to build / design .net applications.Again as Framework class library(FCL) names depicts us its a collection of thousand and thousands of classes which is use to build an application.
The Framework Class Library (FCL) is the collection of libraries that contains the totality: ASP.NET, WinForms,WCF,Web Services, the XML stack, ADO.NET and Many more.
Below image will make things more clear for you :
Some of the FCl libraries are :
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